1. Field of the Invention
The present invention relates to a vehicle vibration damping force control system, and more specifically to a system for controlling a damping force against vehicle vibration such as rolling motion, pitching motion, and bouncing motion.
2. Description of the Prior Art
A prior-art apparatus for damping vehicle rolling motion has been proposed by the same applicant and disclosed in Japanese Published Unexamined (Kokai) Patent App. No. 60-128011. That prior art apparatus comprises damping force adjustable shock absorbers serving as rolling rigidity adjustable mechanisms provided for each vehicle wheel, respectively; a steering angle sensor for detecting steering wheel angles; steering rate calculating means for calculating a steering rate per unit time on the basis of signals of the steering angle sensor; steering rate discriminating means for checking whether a value calculated by the calculating means exceeds a predetermined value; and control means for increasing each rolling rigidity of the shock absorber for each vehicle wheel only when the result discriminated by the discriminating means exceeds a predetermined steering rate.
Further, a prior-art apparatus for damping vehicle pitch motion has been proposed by the same applicant and disclosed in Japanese Published Unexamined (Kokai) Patent App. No. 60-64011. The apparatus for damping vehicle pitch motion comprises means for detecting vehicle brake state; means for checking brake start time and brake end time on the basis of the detected brake state; and control means for momentarily increasing the damping force or the spring constant for at least front wheels or rear wheels at the respective brake start and end times.
In the prior-art vehicle motion damping apparatus, although the damping force for each vehicle wheel can be adjusted according to vehicle behavior such as rolling or pitching motion, since the damping force against various behavior (that is rolling, pitching, bouncing, etc.) is adjusted simultaneously in proportion to the wheel base and/or the vehicle tire tread, there exists a problem in that riding comfort is degraded. For example, when a higher damping force is generated to damp the rolling motion, the damping force against the bouncing motion is simultaneously increased.